This invention relates generally to railroad equipment and more particularly to a sliding boxcar door having a unique construction in which a balsa core is sandwiched between two fiberglass skins and reinforced at the periphery by rigid metal edged stiffeners.
In the past, railroad boxcars have been equipped with steel doors which are expensive, heavy and difficult to handle. Because of the difficulty involved in sliding steel boxcar doors open and closed, machines such as forklifts are commonly used to assist in the opening and closing of the door. The forklift is often jammed into the door, thus causing it to bend and making it even harder to open and close as well as creating other problems.
The present invention is directed to a novel boxcar door having a unique construction which is lighter in weight than a steel door and which avoids other problems associated with the conventional steel boxcar door. In accordance with the invention, a boxcar door panel is constructed by sandwiching a balsa core between two thin fiberglass skins. The edges of the panel are strengthened by steel tubes which are enclosed by the fiberglass skins. By virtue of this construction, advantage is taken of the low cost and light weight of balsa and fiberglass, while the steel tubes provide structural strength and rigidity at the door edges which are the most vulnerable areas of the door.
It is a special feature of the invention that the door panel is constructed with a built-in curvature providing it with a concavo-convex configuration that counteracts the effects of thermally induced warpage. The concave side faces inwardly so that when the outside of the door is heated, the thermal distortion that is thereby induced does not cause the door to bow inwardly beyond the plane of the door frame. As a consequence, thermal warpage does not deform the door enough to cause it to interfere with the door frame and possibly create difficulty in opening and/or closing of the door.